SERVER-12461 Use larger values to test for too large $position arguments.

The previous values were integers that were just 3 away from the largest
possible 64-bit integer, were parsed as the same float as the largest possible
integer, and so were accepted.  This changes them to be 10 times as large.

I observed this failure on an aarch64 / arm64 system.  I don't really understand why it passes on x86.